[CIR][CIRGen][NFC] Support yielding values in LexicalScope

Once the LexicalScope goes out of scope, its cleanup process will also
check if a return was set to be yielded, and, if so, generate the yield
with the respective value.

ghstack-source-id: 9305d2ba5631840937721755358a774dc9e08b90
Pull Request resolved: #312

clang/lib/CIR/CodeGen/CIRGenFunction.cpp

@@ -381,8 +381,10 @@ void CIRGenFunction::LexicalScope::cleanup() {
     if (localScope->Depth != 0) { // end of any local scope != function
       // Ternary ops have to deal with matching arms for yielding types
       // and do return a value, it must do its own cir.yield insertion.
-      if (!localScope->isTernary())
-        builder.create<YieldOp>(localScope->EndLoc);
+      if (!localScope->isTernary()) {
+        !retVal ? builder.create<YieldOp>(localScope->EndLoc)
+                : builder.create<YieldOp>(localScope->EndLoc, retVal);
+      }
     } else
       (void)buildReturn(localScope->EndLoc);
   };

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -1703,6 +1703,9 @@ class CIRGenFunction : public CIRGenTypeCache {
       Switch   // cir.switch
     } ScopeKind = Regular;
 
+    // Track scope return value.
+    mlir::Value retVal = nullptr;
+
   public:
     unsigned Depth = 0;
     bool HasReturn = false;
@@ -1725,6 +1728,8 @@ class CIRGenFunction : public CIRGenTypeCache {
       assert(EntryBlock && "expected valid block");
     }
 
+    void setRetVal(mlir::Value v) { retVal = v; }
+
     void cleanup();
     void restore() { CGF.currLexScope = ParentScope; }